I had a similar problem while rebuilding my VTX, I spent some time trying to find the cause, In my case it turned out to be the locknut on the bearing, the face of the nut was not perpendicular to the thread, it had ~ 0.3mm out of square on 16 dia. I turned up a tight fitting thread in the lathe and ground the face of the nut square to the thread, cured it completely. I did all three nuts while I was at it, none of them were true which surprised me as they were INA nuts hardened and ground and had been on the m/c from new.